1. Field of the Invention
The present invention relates to a computer system using an universal serial bus (USB) and, more particularly, to a method of realizing display power management signaling (DPMS) function of a display device, which confirms the operation state of USB when a display control mode is converted into power off mode in the execution of the DPMS function, thereby preventing errors in the operation of the USB in the mode conversion according to the DPMS operation.
2. Discussion of Related Art
A general computer system includes computer main body (referred to as computer hereinafter) managing information and various peripheral devices processing the information. FIG. 1 shows a configuration of this computer system. Referring to FIG. 1, as input means for inputting information in computer 1, there are keyboard 2 having a plurality of keys and mouse 3 used for forming graphics. A display device 4, output means, displays information transmitted from the computer on its display picture as an image. In addition to, a modem, printer, sound device and scanner are used as computer peripheral devices. Each of these devices must occupy a port obtained from one of slots usable on the motherboard in computer 1. For this, a user is required to open the computer's case and insert interface cards for the slots into the board. Furthermore, there are cases where the user should operate switches, set jumpers, and divide connectors into parallel and serial types. Due to these complicated procedures, users easily give up the setting of new devices. Moreover, since there are limits in the number of slots of the computer, the addition of peripheral devices is not possible when the slots are all occupied.
To meet the demand for more various convenient peripheral devices, a computer system using USB, as shown in FIG. 2, has been developed. FIG. 2 shows USB 10, computer 1, display 4, printer 5, scanner 6 and exterior modem 7. With the use of this USB, the addition of peripheral device becomes very easy, so that there is no need for the user to open the computer case to connect peripheral devices or related cards. Devices like keyboard and display are directly connected to the computer and other peripheral devices are easily connected through extension hubs included in the keyboard and display, or through a separate USB device. These extension hubs provide additional connection sockets and can be connected in tree shape. The peripheral devices may have up to several meters of distance from one another or from the extension hub.
The USB can connect 127 other devices in total to one computer, and transmits 5V of operation voltage, to solve the problem that many peripheral devices currently used consume high AC power. Furthermore, the USB has rapid data transmission rate of 12 Mbit/sec so that it can provide vast processing capability for most peripheral devices having higher band widths only with the cost corresponding to the current connector technique. Accordingly, the USB will become main characteristics in the next computer system. A telephone network, modem, printer, microphone, mouse, scanner and digital camera can be connected through the USB to the computer. The USB has two main effects of simplicity and convenience. The USB detects the addition or removal of device to/from the computer based on information from the computer. This operation can be performed in power-on state, in contrast to the operation of conventional built-in slots. Thus, there is no need to reboot the system. Moreover, the USB supports real plug-and-play operation. The USB automatically determines information about resources such as driver software and bus bandwidth required for each peripheral device, and secures the information to allow the display to use it without interference of the user.
FIG. 3 shows a configuration of the USB in detail. Referring to FIG. 3, USB 10 includes a USB control bus 11 for controlling information transmission between computer 1 and peripheral devices using data and clock provided by display device 4, a DC--DC converter 12 for processing the power supplied from display device 4 to provide operation power to USB control circuit 11 and down stream ports 14, 15 and 16 respectively connected to peripheral devices 5, 6 and 7, and an over-current protection circuit 13 for detecting output current of DC--DC converter 12 to prevent damages due to over-current.
In this configuration, the power (14V) supplied from display device 4 passes through DC--DC converter 12, to be provided to USB control circuit 11 as its operation voltage (5V). Here, display device 4 and USB control circuit 11 are constructed in such a manner that they can transmit data and clock from each other. The power (5V) from DC--DC converter 12 is supplied to USB control circuit 11 and to peripheral devices 5, 6 and 7 through down stream ports 14, 15 and 16. The computer is connected to up stream port of USB 10. In this case, USB environment is set in the computer, and computer 1 automatically supports the USB control environment. When computer peripheral devices 5, 6 and 7 are connected to down streams 14, 15 and 16 of USB 10, computer 1 confirms IDs registered, and automatically installs when there is no error. Accordingly, the user can use the peripheral devices without separate operation.
Display device 4, a typical peripheral device of the computer, displays signals transmitted from computer 1 as images to allow the user to be able to recognize it. FIG. 4 shows a basic configuration of the inner circuit of the display device. Referring to FIG. 4, the inner circuit of the conventional display includes: a video card 210, installed in a computer (not shown), for providing color signals (R,G,B) required for color formation and horizontal/vertical synchronous signals (H.sub.-- Sync/V.sub.-- Sync); a microcomputer 220 for receiving the horizontal/vertical synchronous signals from video card 210, and generating a picture control signal for controlling a monitor picture; vertical deflection circuit 230 and horizontal deflection circuit 240 for receiving the horizontal synchronous signal (H.sub.-- Sync) and vertical synchronous signal (V.sub.-- Sync) and performing horizontal deflection and vertical deflection to enable electron beam generated by an electron gun of a CRT 280 to be sequentially deflected starting from the top of the left portion of CRT 280 to the bottom of its right portion by a defection yoke, thereby forming an image like one picture; a high voltage circuit 250 for supplying a high voltage to the anode of CRT 280 using a blanking pulse generated from the output port of horizontal deflection circuit 240 according to the principle of switching circuit and high voltage technique; a video pre-amplifier 260 for amplifying a low-level image signal (R,G,B) transmitted from video card 110 with a low voltage amplifier, to maintain the signal at a specific voltage level; and a video main amplifier 270 for amplifying the signal amplified by video pre-amplifier 260 to 40 Vpp to 60 Vpp of signal, to supply energy to each pixel of the display.
In this display device, the images are formed using electron beam projected on the fluorescent screen. Here, a circuit which converts the deflection of the electron beam is called deflection circuit. According to "DPMS PROPOSAL", which was published and distributed in U.S.A. Jan. 26, 1993, the operations of the horizontal/vertical deflection circuits can be controlled using horizontal synchronous signal HS and vertical synchronous signal VS supplied to display device 4 from computer 1. Here, computer 1 selectively applies the horizontal synchronous signal HS and vertical synchronous signal VS to display device 4, to operate display device 4 in one control mode of normal mode, stand-by mode, suspend mode and power off mode.
The normal mode is for normal supplying power to display device 4. In the stand-by and suspend modes, video signals, processed by the video processor of the display, are muted, so as not to be displayed. Here, the stand-by mode and suspend mode cut off the horizontal synchronous signal HS and vertical synchronous signal VS, respectively. The power off mode is for cutting off the power supply to display device 4. This control mode is sequentially converted from the normal operation mode, stand-by mode, suspend mode to power off mode, corresponding to a period during which the computer system is not used.
Accordingly, the display device detects if the horizontal and vertical synchronous signals HS and VS are received from the computer, and executes corresponding power saving mode. However, there are problems in the realization of the DPMS function of the display using the USB. As described above, the USB operates based on the power provided by the display device. If the display operates in the power off mode according to the DPMS function, only 8 W approximately is supplied to the display. Thus, the USB cannot be normally operated because sufficient power is not supplied from the display device normally.